1. Field of the Invention
The present invention relates to an image file generation device that generates an image file for recording from multi-gradation image data, and an image file display device that displays the image file.
2. Description of the Related Art
There are a portable terminal such as a digital camera and a smartphone, a TV, and various monitors, each of which is provided with a liquid crystal display device as an image display device in many cases. The liquid crystal display device includes a liquid crystal panel in which liquid crystal elements with adjustable light transmittance are arranged to form a two-dimensional array, and a backlight (device) that irradiates the liquid crystal panel with light.
In recent years, there has been known a liquid crystal display device that includes a plurality of illumination sections capable of individually illuminating each of a plurality of areas formed by dividing a display area of a liquid crystal panel, and that performs local dimming control (or area control) to independently control brightness of each of the illumination sections. The local dimming control is performed to increase contrast feeling in a case where an image locally includes an area with low brightness and an area with high brightness, thereby enabling capability of reproducing gradation in an area with particularly low brightness (hereinafter referred to as a shadow portion) to be improved.
In a case where data of an image photographed with a digital camera is displayed on a liquid crystal display device that performs the local dimming control above (hereinafter referred to as simply a liquid crystal display device), a conventional digital camera records photographed image data at 8-bit, so that the number of gradations of photographed image data in a shadow portion is not enough. Thus, there has been a problem in which it is impossible to take advantage of performance of a liquid crystal display device with a wide dynamic range cannot be taken, so that even a liquid crystal display device with improved capability of reproducing gradation (such as 10-bit) has the same image quality of a photographed image to be displayed as image quality of a conventional liquid crystal display device.
In a digital camera described in Japanese Patent Application Laid-Open No. 2011-250464 (hereinafter referred to as PTL 1), photographed image data is recorded in a plurality of formats such as a RAW (non-compression recording format) and a JPEG (compression recording format). The RAW data ensures the sufficient number of gradations in a shadow portion, so that it is possible to display the shadow portion of the photographed image at sufficient gradation on the basis of the RAW data.
In an image processing apparatus described in Japanese Patent Application Laid-Open No. 2008-301010 (hereinafter referred to as PTL 2), in order to display 8-bit input image data in a liquid crystal display device capable of 10-bit gradation display, α-bit expansion is applied to input image data, and then data smoothing is applied to the input image data. Accordingly, it is possible to increase the number of effective gradations of the 8-bit input image data.
In an image recording method described in “KODAK PROFESSIONAL DCS Pro SLR_n ERI-JPEG” (hereinafter referred to as NPL 1), difference data between 12-bit RAW data and 8-bit JPEG image data is acquired so that the JPEG image data and the difference data are recorded in the same image file. Since image data equivalent to the RAW data can be acquired from the JPEG image data and the difference data, it is possible to display a shadow portion at sufficient gradation.
An image recorder described in Japanese Patent Application Laid-Open No. 2001-203970 (hereinafter referred to as PTL 3) performs steps of: converting 14-bit gradation information (image data) into 8-bit gradation information; and converting the 14-bit gradation information into 12-bit gradation information with conversion characteristics in which reproducing characteristics on a low brightness side is emphasized. Next, the image recorder performs steps of: acquiring difference information between the 12-bit gradation information and the 8-bit gradation information described above; and associating the 8-bit gradation information and the difference information with each other so that the information is stored. Accordingly, since 12-bit gradation information can be generated on the basis of the 8-bit gradation information and the difference information, it is possible to display a shadow portion at sufficient gradation.
In an image processing apparatus described in Japanese Patent Application Laid-Open No. 2010-278889 (hereinafter referred to as PTL 4), after a parameter is set to divide input image data into a dark image area and a light image area, if a bit number of the input image data is more than a predetermined quantization bit number, a density map is generated in accordance with the parameter above to show which of the dark image area and the light image area each of pixels in the input image data belongs to. Subsequently, the image processing apparatus quantizes each of the pixels at a quantization bit number corresponding to an area to which each of the pixels belongs, on the basis of the density map and the quantization bit number, described above, to generate quantization data on the basis of each of the quantized pixels. Accordingly, since it is possible to favorably hold data of a shadow portion to be lost at the time of conventional encoding, the shadow portion can be displayed at sufficient gradation in a liquid crystal display device.